“If you turn away your foot from the Sabbath,
From doing your pleasure on My holy day,
And call the Sabbath a delight,
The holy day of the Lord honorable,
And shall honor Him, not doing your own ways,
Nor finding your own pleasure,
Nor speaking your own words,
Then you shall delight yourself in the Lord;
And I will cause you to ride on the high hills of the earth,
And feed you with the heritage of Jacob your father.
The mouth of the Lord has spoken.”

What a promise! A great blessing hinges on honoring the Sabbath. But why? I understand the Sabbath was established at creation. We rest because God rested, and certainly, we need rest for many reasons. Further, we need time to detach from our earthly concerns to dwell upon godly concerns. The benefits seem self-evident (delight in the Lord), but limited to spiritual well-being; being at peace with God. But this promise is more than that (ride high on the hills, feed on Jacob's heritage), so why does the Sabbath make or break it?

There is another important factor that distinguishes Shabbat from Yom Tov. The day of Yom Tov is decided by the people (they establish the calendar.) Shabbat, however, is decided by G-d, and it is a holiday that occurs every 7th day. Man has no control over its date. So, stopping your work on Shabbat, in a sense, requires conscious "work" and a continuous affirmation of your faith and belief in G-d that HE controls time. You are consciously devoting that space of time in your week to G-d, regardless of your own needs and desires that may conflict.
– DanFSep 18 '17 at 18:13

3 Answers
3

First, let me note that the passage you quoted comes after some other Divine expectations. It's not saying that only Shabbat is important, but it clearly is saying that Shabbat is important. I'll focus on Shabbat here since that's what you asked about, but I do encourage you to read the whole chapter for additional context.

God tells Moshe in the torah that Shabbat is a sign between God and Israel. While all mitzvot and all special days (like festivals) are important, only Shabbat gets this specific designation. We are to set aside even the work of building the mishkan, God's "dwelling place" on Earth, and the penalty for violating Shabbat is death and having one's soul cut off. From Shemot 31:13-17:

'Speak thou also unto the children of Israel, saying: Verily ye shall keep My sabbaths, for it is a sign between Me and you throughout your generations, that ye may know that I am the LORD who sanctify you.
Ye shall keep the sabbath therefore, for it is holy unto you; every one that profaneth it shall surely be put to death; for whosoever doeth any work therein, that soul shall be cut off from among his people. [...]
Wherefore the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant.

Rashi says about the sign:

For it is a sign between Me and you: It is a sign of distinction between us that I have chosen you, by granting you as an inheritance My day of rest for [your] rest.

Whole books have been written on the spiritual benefits of Shabbat. I humbly add an idea of my own: one purpose of a sign is to be visible. Shabbat is a regular, weekly occurrence -- way more visible both to Jews and others than festivals and other special days. Shabbat is a regular event, which requires special care. It's pretty much impossible to be Shabbat-observant "stealthily" -- by committing to Shabbat you're telling your employer, your customers (if you own a business), your neighbors, your friends, and anybody else who knows you that you keep Shabbat, which you do because you keep the torah that God gave us. As somebody who did not always keep Shabbat (and is still learning some of the finer points), I can tell you that having to make this weekly affirmation strengthens my dedication and resolve.

And it's not just about individual benefits. The whole community stopped building the mishkan to keep Shabbat. Our whole communities leave work, close businesses, set aside computers, and come together on Shabbat, ideally to make it a delight, but also to help and reinforce each other. I think one of the reasons that Shabbat hospitality is such a common thing when doing outreach (kiruv) is that it ties people who are a little more marginal into a community doing Shabbat.

The command to keep Shabbat gets extra emphasis from God compared to other mitzvot. Shabbat is a sign, a public declaration, and a frequent occurrence. It enriches the individual and the community.

A proper answer to this question would fill books. I will focus on the scripture you referred to.

There are promises and blessings associated with keeping the Sabbath. The Lord will:

1) cause (the Sabbath keeper) to ride upon the high places of the earth,
2) feed (the Sabbath keeper) with the heritage of Jacob.

These blessings relate to our relationship with the Lord and the Torah.

1) The "high places" in the Tanakh are nearly universally sites of idolatry and therefore the subject of great condemnation. But the Tanakh also mentions, the high places as the Lord's domain:

Job 25:2 KJV - Dominion and fear [are] with him, he maketh peace in his high places.

Amos 4:13 KJV - For, lo, he that formeth the mountains, and createth the wind, and declareth unto man what [is] his thought, that maketh the morning darkness, and treadeth upon the high places of the earth, The LORD, The God of hosts, [is] his name.

In Amos 4 (above) we have a connection between the Lord's creation, His giving man His word and the high places (which in my opinion is metaphorically, where we meet God).

Habakkuk 3:19 KJV - The LORD God [is] my strength, and he will make my feet like hinds' [feet], and he will make me to walk upon mine high places.

This is where His next blessing comes in!

Deuteronomy 33:3-4 Yea, he loved the people; all his saints [are] in thy hand: and they sat down at thy feet; [every one] shall receive of thy words. Moses commanded us a law, [even] the inheritance of the congregation of Jacob.

So, what is one of the many reasons the Sabbath is so important? Because it brings us into closer union with the Lord. As Isaiah 58:13-14 explains, in it:

we will not do our own ways -- but the Lord's ways
we will not seek our own pleasures - but the Lord's pleasures,
we will not speak our own words -- but the Lord's words

Then...
We will delight, [more and more] in the Lord
We will meet with Him in communion on His holy day
We will be given more insight from Torah (the heritage of Jacob)!

A lifetime of Sabbaths afford the non-scholar the opportunity to spend 16 uninterrupted, waking hours a week of time with the Lord and His word, leading to understanding and knowing the Lord and filling your life with the delight of His word.

Thus saith the LORD, Let not the wise [man] glory in his wisdom, neither let the mighty [man] glory in his might, let not the rich [man] glory in his riches: But let him that glorieth glory in this, that he understandeth and knoweth me, that I [am] the LORD which exercise lovingkindness, judgment, and righteousness, in the earth: for in these [things] I delight, saith the LORD. - Jeremiah 9:23-24 KJV

But his delight [is] in the law of the LORD; and in his law doth he meditate day and night. - Psalm 1:2 KJV

Psalm 119:35, 77, 174 KJV
Make me to go in the path of thy commandments; for therein do I delight.
Let thy tender mercies come unto me, that I may live: for thy law [is] my delight.
I have longed for thy salvation, O LORD; and thy law [is] my delight. -

And I will give them an heart to know me, that I [am] the LORD: and they shall be my people, and I will be their God: for they shall return unto me with their whole heart. Jeremiah 24:7

R Akiva Tatz has a beautiful explanation on this. He starts by asking why all holidays happen once a year but Shabbat is every week. What is it that we need to be reminded of every week?

He responds that Shabbat is an opportunity to reflect on one's achievements during the week and to check we are indeed directing our lives in the proper way.

Shabbat is called “me’eyn olam ha’ba” – a small degree of the experience of the next world. Just as the one who eats on Shabbat is the one who prepared in advance (see Avoda Zara 3a), the one who enjoys the world to come is the one who prepared in this world. Shabbat breaks the illusion of immortality. There are never more than 7 days before Shabbat reminds us to take stock of where we stand in relation to Torah and mitzvot.

So to answer your question, Shabbat brings blessing because it keeps us focused on what matters and enables us to fully benefit from our rewards in the world to come. As the prophet says in the verse you quote: "then you shall delight yourself in the Lord".